This invention relates to a valve that resets itself, to a combination of the valve and a double acting air cylinder, and to a lock that is controlled through such a valve.
A significant expense in the operation of many large buildings is that of security. To reduce this expense as well as to improve security, many large buildings have doors which are both remotely controlled and remotely monitored. Normally, a large building of the type under consideration has a security office, and from that office doors at critical locations throughout the building are monitored. Many of the doors have locks which are likewise controlled from the single security location.
Perhaps the most common type of remotely controlled lock is the strike-centered variety. A lock of this nature has a keeper or strike which is actuated by a solenoid and when actuated releases the lock bolt that normally projects into it from the door. Strike-centered systems are easily defeated, and therefore do not provide a high degree of security.
Moving the solenoid actuator to the lock itself, that is, into the door, enhances the degree of security. In such a system, the solenoid normally pulls the lock bolt or else releases the lock bolt so it can thereafter be retracted by turning a knob. Since the solenoid is within the door itself, electric wires must be run from the door frame into the door, which is usually not much of a problem. However, Underwriters Laboratories will not approve an installation requiring more than 100 voltamperes, and as a consequence the solenoids are capable of exerting only a very small force. Indeed, at this low power, it is practically impossible to utilize a solenoid for pulling a lock bolt out of its keeper.
Due to the electrical power limitations on doors, some installations now employ compressed air to operate the remotely controlled locks. Normally, buildings of the type under considerations have compressed air lines for operating other equipment, primarily in the heating and air-conditioning systems, so the compressed air is readily available. An air cylinder operating under a moderate pressure furnishes a significantly greater force than a solenoid and is furthermore much more reliable. Perhaps, the best way to bring compressed air into a door is through one of the hinges on which the door is mounted, and a hinge suitable for this purpose is disclosed in U.S. Pat. No. 3,872,541. That hinge, however, is capable of accommodating only one air line, which is adequate for single acting cylinders, but not double acting cylinders. Two hinges are required by the latter, but the hinges are expensive in their own right and are furthermore expensive to install. Indeed, in such an instance two holes extending transversely through the door, would be required, with each hole originating at a different hinge and terminating at the mortise for the door lock.